1. Field of the Invention
The present invention relates generally to nuclear waste consolidation apparatus, and, more particularly, to apparatus for consolidating spent nuclear fuel rods into high density arrays.
2. Description of the Prior Art
Commercial nuclear reactor facilities generate electrical power by converting the heat energy given off during a nuclear fission process into electrical energy. Conventionally, nuclear fuel rods filled with fissionable material are employed as the fuel source to fuel the heat-producing nuclear reaction required for the generation of such power. The fuel rods are typically metal tubes filled with a fissionable, nuclear fuel material, and are about 0.4-0.6 inch in diameter and from 8 to 15 feet in length. Groups of such fuel rods are assembled in a fuel rod assembly which includes grids for alignment and support of the fuel rods, a lower end fitting, an upper end fitting, and guide tubes. Within the fuel rod assembly, the individual fuel rods are spaced-apart in a pre-established array, usually a rectangular array, and are spaced-apart in the array at precise locations.
The entire fuel rod assembly containing the array of nuclear fuel rods is introduced into a nuclear reactor core whereat controlled fission is allowed. After the nuclear fuel in the fuel rod assembly is spent to a pre-established level, the "spent" fuel rod assembly is removed from the reactor core and replaced by a new fuel rod assembly. Once removed, the spent fuel rod assembly is stored vertically in a storage rack in an underwater storage area until the radioactive properties of the individual rods and the associated support structure have dissipated.
Presently, spent nuclear fuel rod assemblies are stored without any deliberate change in the structures thereof. Over the course of time, however, more and more spent fuel rod assemblies have been stored in these underwater storage areas; the remaining available space for storing additional spent fuel rod assemblies is decreasing.
Increasing the density of the material stored in the underwater storage areas allows a greater amount of nuclear waste material to be stored in the limited available space of such storage areas. To accomplish this end, a number of suggestions have been made for removing previously stored fuel rod assemblies from the pool, withdrawing the individual spent fuel rods from the assemblies, and thereafter assembling the individual spent fuel rods in new containers or canisters wherein the fuel rods are more densely compacted. These more densely compacted canisters may be returned to the underwater storage areas, and the remaining fuel assembly skeletons dismantled or otherwise disposed of, thereby more efficiently using the limited available space of the underwater storage areas.
In practice, presently proposed compacting processes suffer from inherent difficulties due to the actual configuration of spent nuclear fuel rods after long-term exposure in the nuclear reactor core. In some cases, the fuel rods become twisted and bent out of alignment, sometimes as much as 1.5 inches in an 8-foot long rod.
A further problem exists in that the long, thin fuel rods are difficult to manipulate.
Still further, an additional problem relates to the inherent safety of compacting spent fuel rods. There is a possibility that the fuel rods might become spaced apart by a critical distance while removed from the fuel rod assembly and before compaction and confinement in a storage canister. Such a possibility should be precluded. A final problem involves accountability of the spent fuel material from a nuclear safe-guards point of view.
It is, therefore, an object of the present invention to provide an apparatus to allow the safe compaction of spent nuclear fuel rods from a density corresponding to the density of the fuel rods in a fuel rod assembly to a compacted configuration in which the density is much greater.
It is a further object of the present invention to provide an apparatus which allows the location and identity of each spent fuel rod to be determinable during storage thereof.